Issue 36

T. Fekete, Frattura ed Integrità Strutturale, 36 (2016) 99-111; DOI: 10.3221/IGF-ESIS.36.10

o The other type of the model was designed for elastic or elastic-plastic calculations with a crack embedded into the mesh; it is the 3D FE model of the lower cylindrical part of the vessel with the bottom, including a crack embedded into the mesh. The model was developed with the purpose of simulating through wall temperature, stress and strain distributions occurring during PTS transients, and also performing subsequent fracture mechanics calculations on the embedded crack. The FE mesh models the welds, and includes quadratic, iso-parametric brick-type elements with 20 nodal points. The model was designed to study plasticity effects too. The developed model contains 160 540 elements and 709 826 nodal points. The geometrical model is presented on Fig. 5. The crack location was selected after long series of calculations performed on the simpler model, in order to reduce the time-consuming work of developing a mesh around the crack front. The crack model is an underclad, semi-elliptical crack with a=14 mm, a/c=1/3; the crack model is shown on Fig. 5 below.

Figure 5 : 3D Finite element model of a lower cylindrical part with embedded crack of a VVER-440 RPV.

Description of neutron-transport calculations: The fluence data were provided by full 3D neutron-transport calculations that took the full loading-history of the energetic core into account. This fact made a complete re-evaluation of material ageing possible. Materials, constitutive models:  Both the cladding and the ferritic materials (15Ch2MFA forging and the weld metal) were modeled during calculations. For thermal and strength calculations, the data were derived from the manufacturer’s documentation.  In thermal calculations, the thermo-physical parameters were temperature-dependent.  In thermo-mechanical strength calculations, the Neumann-Duhamel constitutive model was used with temperature dependent parameters of the manufacturer’s documentation. In the case of elastic-plastic calculations, plastic material properties were derived from the re-evaluation of the material tests performed in the frame of the manufacturer’s surveillance program.  For describing the fracture toughness of the structural materials, the equation:

107